Stabilization of thermally unstable liquid hydrocarbon fuels



United States Patent 3,218,137 STABILIZATION 0F THERMALLY UNSTABLELIQUID HYDROCARBON FUELS George Belo, Franklin Township, AlleghenyCounty, and Arthur V. Churchill, Oakmont, Pa., assignors to GulfResearch & Development Company, Pittsburgh, Pan, a corporation ofDelaware No Drawing. Filed Dec. 28, 1960, Ser. No. 78,853

20 Claims. (Cl. 4466) This invention relates to improving the thermalstability of combustion gas turbine fuels. More particularly, theinvention relates to reducing the tendency of combustion gas turbinefuels to form solid deposits at very high service temperatures byincorporating therein small amounts of a monoester of a higher fattyacid and diethylene glycol.

Combustion gas turbine fuel is presently employed as a cooling medium,or heat sink, in combustion gas turbine powered aircraft to remove heatby indirect heat exchange from lubricating oil that has absorbed heatdeveloped in the engine by the compression of combustion air, by fuelcombustion, and by friction of moving parts. As a result, the fuel issubjected to heat transfer surface temperatures during service of theorder of 300 to 400 F. for relatively substantial time intervals. Inaddition, the fuel is subjected to even higher temperatures, of theorder of 500 F., for short periods of time in the area of the nozzles ororifices from which the fuel is introduced into the combustion chamberof the engine. As a result, certain components of the fuel tend toundergo decomposition due to polymerization, oxidation, and thermaldecomposition, and to form solid or semi-solid degradation products thatclog the fuel orifices and thereby interfere with proper combustion ofthe fuel. Ordinary stabilizing agents, antioxidants and the like, of thekind that are employed to stabilize the fuels during storage have beenfound inadequate to inhibit deterioration of the fuels at the highservice temperatures encountered in aviation turbine engines.

The present invention relates to improving the thermal stability ofliquid hydrocarbon combustion gas turbine fuels, such as aviationturbine fuels, and more particularly to reducing the tendencies of suchfuels to form deposits on heat transfer surfaces at temperatures inexcess of 300 F. and in the fuel inlet regions of the combustion zonesof the engines in which the fuels are consumed, whereby such fuels arerendered more suitable for use in combustion gas turbine engines. It hasbeen found that the thermal stability characteristics of theabove-indicated fuels, as well as other characteristics of these andother hydrocarbon oils, can be improved by incorporating therein a smallamount of a monoester of a fatty acid that contains 8 to 18 carbon atomsand diethylene glycol. In a preferred embodiment the monoester is theester of lauric acid, but monoesters of other fatty acids includingsaturated acids such as Oxo-octanoic, palmitic, stearic, oleic,linoleic, and linolenic acids can be used. When protection also isdesired against clogging of fuel orifices due to thermal degradation ofthermally unstable fuel contacted by the hot fuel orifices under hightemperature service conditions, without sacrificing the exceptionalprotection against fouling of heat transfer surfaces provided by thediethylene glycol monoesters alone, there can also be included in thefuel compositions of this invention a supplemental anticlogging agentsuch as (I) an oil-soluble,

ice

nitrogenous, anticlogging copolymer containing as its essentialmonomeric components in a weight ratio of about 0.03 to 1:1, preferably0.05 to 0.75:1 (a) a copolymerizable alkyl ester of an acid such asacrylic and lower alkacrylic acids whose alkyl ester substituentcontains 8 to 18 carbon atoms, and (b) a copolymerizable unsaturatedcompound containing one ethylenic linkage copolymerizable With theaforesaid alkyl ester and a nitrogen-containing substituent group thatis not polymerizable with said alkyl ester, such as amine salts,quaternary ammonium salts or aminoesters of acrylic or lower alkacrylicacids, or (II) an oil-soluble phosphosulfurized hydrocarbon anticloggingagent obtained by reacting a phosphorus sulfide with an aliphatichydrocarbon. A specific example of a preferred copolymer is the 1:9weight ratio copolymer of di-Oxo-octyl)aminoethyl methacrylate andlauryl methacrylate, but other copolymers having their extralinearnitrogen substituents linked to the polymer chain through a linkageother than an ester linkage, for example, a quaternary ammonium saltlinkage or an amine addition salt linkage, including the dehydrated oramido form of such amine salt linkage, can be used. Specific examples ofsuch other copolymers include the 1:9 weight ratio copolymer ofsoyaalkyltrimethylammonium methacrylate and lauryl methacrylate and the1:9 weight ratio copolymer of di(Oxo-octyl) ammonium methacrylate andlauryl methacrylate. A specific example of an oil-solublephosphosulfurized aliphatic hydrocarbon is the phosphosulfurized productobtained by reacting P S with pentapropylene, but the phosphosulfurizedproducts obtained by reacting other phosphorus sulfides and otheraliphatic hydrocarbons, including other olefin polymers, can be used.The diethylene glycol monoesters are ef fective as such to reduce heattransfer surface deposits, and, in combination with the supplementalanticlogging agents disclosed herein they are effective to reduce fuelnozzle deposits when employed in small amounts. Proportions in the rangeof 10 to 20 pounds of each material per 1,000 barrels of fuel arepreferred but other proportions, for example, as little as about 2.5pounds or more per thousand barrels of fuel, can be used. When thesupplemental anticlogging agents are employed in conjunction with thediethylene glycol monoesters disclosed herein, the respective materialscan be used in varying proportions with respect to each other. Therespective materials are preferably added to the fuels in about equalproportions by Weight, but other proportions can be used provided thecompound present in the smaller amount is present in an amountcorresponding to at least about 2.5 pounds per thousand barrels of fuel.Ordinarily, the respective materials will be employed in Weight ratiosof about 1:4 to 4:1, but other weight ratios, for example, 1:8 to 8:1can be used.

The exact manner in which the diethylene glycol monoesters disclosedherein function to improve the thermal stability of combustion gasturbine fuels has not been definitely determined. Inasmuch as thediethylene glycol monoesters disclosed herein effect a substantiallygreater reduction in the heat transfer surface deposits than in fuelnozzle deposits, it is clear that the inhibitive mechanism involved ishighly selective. In view of the distinct nature of the heat exchangersurface deposits and the fuel orifice deposits, as evidenced by thefailure of the diethylene glycol monoesters greatly to reduce bothdeposits, it might be supposed that the diethylene glycol monoestersdisclosed herein and the anticlogging agents, when the latter areemployed, function independently of one another. However, this iscontradicted by the fact that some materials that are effective as suchto inhibit fuel nozzle deposits in combustion gas turbine fuels, havebeen found ineffective to inhibit such deposits in the presence ofdiethylene glycol monoesters. The fact that normally effectiveanticlogging agents are not necessarily effective to inhibit fuel nozzledeposits in the presence of the diethylene glycol monoesters suggestsstrongly an interaction between the monoesters and the anticloggingagents disclosed herein.

Although it is clear that heat transfer surface deposits and fuel nozzledeposits differ markedly from each other, it should be noted in passingthat each of these types of deposits also differs, respectively, fromdeposits formed from fuels at low temperatures, that is, below 300 F.The distinction between lowor moderate-temperature deposits and the hightemperature deposits with which the present invention is concerned isemphasized by the fact that many of the distillate fuels that arebenefited by the use of the improvement agents disclosed herein form nodeposits whatsoever at temperatures significantly below 300 F. and alsoby the fact that many improvement agents that are effective to reducedeposits formed in hydrocarbon oils that are unstable at temperaturesbelow about 300 F. have no effect whatsoever in reducing deposits formedin combustion gas turbine fuels at higher temperatures.

The diethylene glycol monoesters disclosed herein can be prepared in anyconvenient manner, for example, by transesterification of the glycerideof a selected fatty acid or mixture thereof containing 8 to 18 carbonatoms with diethylene glycol in a 1:1 mol ratio in the presence of asodium hydroxide catalyst. An example of a preferred diethylene glycolmonoester is diethylene glycol monolaurate. Examples of other diethyleneglycol monoesters whose use is included by this invention are diethyleneglycol mono-Oxo-octanoate, mono-Oxotridecanoate, monopalmitate,monostearate, monooleate, monolinoleate, and monolinolenate.

Any suitable anticlogging agent can be used to supplement the heattransfer surface deposit inhibiting properties of the diethylene glycolmonoesters disclosed herein. That is, any nozzle-clogging inhibitor canbe used that will reduce deposition of thermal degradation fuel depositsin the fuel inlet area of a combustion gas turbine engine in thepresence of the diethylene glycol monoesters disclosed herein, withoutsignificantly detracting from the advantageous properties of suchmonoesters. As indicated, good results are obtainable with variouschemical types of nozzle clogging inhibitor agents, includingoil-soluble, nitrogen-containing copolymers and oil-solublephosphosulfurized hydrocarbons.

The anticlogging nitrogenous copolymers disclosed herein can be preparedin any convenient way. For example, such copolymers can be prepared byreacting the desired monomers in Weight ratios of about 0.03 to 1 partby weight of the nitrogen-containing monomer for each part by weight ofthe nitrogen-free alkyl ester monomer, in the presence of a diluent,preferably a solvent, such as toluene, benzene, ethyl acetate, or othersolvents having similar chain transfer activity, at a temperature in therange of -75 C. to 150 C., preferably C. to 150 C.-, in the presence ofa few hundredths percent to 2 percent, preferably 0.2 to 1.0 percent, ofa free radical catalyst such as benzoyl peroxide, lauroyl peroxide, oralpha-alpha'-azodiisobutyronitrile, preferably in the substantialabsence of oxygen, until the rate of formation of larger polymermolecules has declined substantially, usually after about 3 to hours, asdetermined by periodic sampling of the reaction mixture and observingthe same for the absence of further significant increases in viscosity.

The alkyl acrylate or alkyl alkacrylate ester monomers from which thenitrogenous anticlogging copolymers disclosed herein are prepared can berepresented by the gen eral formula: CH =CRCOOR where R is hydrogen or alower alkyl radical such as methyl, and R is a straight or branchedchain alkyl group containing 8 to 18 and preferably 12 to 18 carbonatoms, such as lauryl, Oxotridecyl, n-hexadecyl, or n-octadecyl.

The nitrogenous monomers from which the copolymers disclosed herein arederived are copolymerizable, unsaturated compounds containing anethylenic linkage that is copolymerizable with the acrylate oralkacrylate monomers and a nitrogen-containing substituent group that isnot copolymerizable with the acrylate or alkacrylate monomers. Thenitrogen containing substituent group can be associated with the groupcontaining the copolymerizable ethylenic linkage through an esterlinkage, a salt linkage, including quaternary ammonium salts and amineaddition salts, as Well as the dehydrated form of the latter, that is,ar'nides.

When the nitrogenous substituents are linked to the polymer chainthrough a quaternary ammonium salt linkage, the nitrogenous monomer willbe a quaternary ammonium salt of acrylic acid or a lower acrylic acidsuch as methacrylic acid, one of whose four covalent N-bonds is attachedto a monovalent aliphatic hydrocarbon radical containing 8 to 18 andpreferably 12 to 18 carbon atoms, two other of whose covalent N-bondsare attached to monovalent aliphatic hydrocarbon radicals containing 1to 18 carbon atoms, or aralkyl radicals containing 7 to 23 carbon atoms,and whose remaining covalent N-bond is attached to an alkyl groupcontaining 1 to 4 carbon atoms. The preferred quaternary ammonium saltmonomers from which the herein-described copolymers can be prepared canbe represented by the general formula:

CHz=CRCOON where R is as defined above, R is an alkyl, alkenyl, oralkadienyl radical containing 12 to 18 carbon atoms, such as lauryl,myristyl, n-hexadecyl, n-octadecyl, n-octadecenyl, or n-octadecadienyl,and R" and R' are radicals of the same kind as R or alkyl radicalscontaining 1 to 4 carbon atoms such as methyl, ethyl, propyl, or butyl,or a mononuclear alkyl radical containing 7 to 23 carbon atoms such asbenzyl, tolylethyl, or a polypropylated aralkyl radical such asp-tetrapropylbenzyl, and R"" is an alkyl radical containing 1 to 4carbon atoms. A specific example of a preferred anticlogging quaternaryammonium salt copolymer is the 1:9 weight ratio copolymer of monomericmixed octadecenyland octadecadienyltrimethylammonium methacrylate andmonomeric lauryl methacrylate. Examples of other quaternary ammoniumsalt copolymers whose use is included by the invention are the 1:9weight ratio copolymers of monomeric distearyldimethylammoniummethacrylate and monomeric lauryl methacrylate and the 0.05:1, the0.121, the 0.5 :1, and 1:1 weight ratio copolymers of monomericdioctadecenyldimethylammonium, octadecenyldimethylethylammonium,distearyldimethylammonium, laurylbenzyldimethylammonium,lauryldimethyl(ethylbenzyl)ammonium acrylates and methacrylates, andmonomeric n-octyl, lauryl, Oxo-octyl, 2-ethylhexyl, Oxo-tridecyl, andn-hexadecyl acrylates and metha-crylates. Quaternary ammonium saltcopolymers of the kind disclosed herein are described and claimed assuch in copending application Serial No. 862,056, filed December 28,1959.

When the nitrogen-containing substituent group is attached to thecopolymerizable ethylenic linkage-containing portion of the monomersthrough an addition salt linkage or the like, the nitrogen-containingmonomers from which the anticlogging copolymers disclosed herein can bederived will be monomeric nitrogen-containing salts formed fromsubstantially equivalent proportions of an acrylic or lower alkylacrylic acid such as methacrylic acid and an amine having as at leastone N-substituent an aliphatic hydrocarbon radical containing 8 to 18carbon atoms, The other N-substituents can be the same as or differentfrom the first-mentioned N-substituent, for example, the otherN-substituents can be hydrogen, aliphatic hydrocarbon radicalscontaining 1 to 18 carbon atoms, or alkylol groups containing 1 to 4carbon atoms. The preferred amine salt monomers from which thenitrogenous addition salt-containing copolymers disclosed herein areprepared can be represented by the general formula:

where R is hydrogen or a lower alkyl radical such as methyl RI N412.

is a secondary or tertiary amine, R is an alkyl, alkenyl, or alkadienylradical containing 8 to 18 carbon atoms, such as lauryl, myristyl,n-hexadecyl, n-octadecyl, n-octadecenyl, or n-octadecadienyl, and R" isan alkylol group containing 1 to 4 carbon atoms such as ethylol orpropylol or an aliphatic hydrocarbon radical containing 1 to 18 carbonatoms such as methyl, propyl, butyl, or any of those named in thedescription of R, and R'" is hydrogen or a radical of the same kind asR". An example of a preferred anticlogging copolymer in which thenitrogencontaining substituent is linked to the polymer chain through anaddition salt linkage is the 1:9 weight ratio copolymer of monomericdi(Oxo-octyl)ammonium methacrylate and monomeric lauryl methacrylate.Examples of other such copolymers are the 3:7 weight ratio copolymer ofmonomeric di(Oxo-octyl) ammonium methacrylate and monomeric laurylmethacrylate, the 1:9 Weight ratio copolymer of monomericdi(Oxo-octyl)hydroxyethylammonium methacrylate and monomeric laurylmethacrylate, and the 0.05:1, 0.1: 1, 0.511, and 1:1 weight ratiocopolymers of monomeric octylammonium, dioctyl ammonium,trioctylammonium, laurylammonium, octadecylammonium, octadecenylammoniumacrylates and methacrylates and monomeric n-octyl, lauryl, Oxo-octyl,2-ethylhexyl, Oxo-tridecyl, and n-hexadecyl acrylates and methacrylates.Amine salt copolymers of the kind disclosed herein are described andclaimed as such in combination with liquid hydrocarbon fuels incopending application Serial No. 33,934, filed June 6, 1960.

When the nitrogen-containing substituent of the monomers from which theanticlogging copolymers disclosed herein are derived is associated withthe polymer chain through an ester linkage, the nitrogen-containingmonomer will be a monomeric ester of acrylic acid or a lower alkacrylicacid such as methacrylic acid and an amine having as at least oneN-substituent an alkylol group, normally containing 2 to 4 carbon atoms,and as another N-substituent an aliphatic hydrocarbon radical containing1 to 18 carbon atoms and as the third N-substituent hydrogen, analiphatic hydrocarbon radical containing 1 to 18 carbon atoms or analkylol radical containing 1 to 4 carbon atoms. The preferrednitrogen-containing ester monomers from which the copolymers disclosedherein are derived can be represented by the general formula:

6 where R is hydrogen or a lower alkyl radical such as methyl, where nis an integer of 2 to 4, preferably 2, R is an alkyl, alkenyl, oralkadienyl radical containing 8 to 18 carbon atoms, such as Oxo-octyl,lauryl, myn'styl, nhexadecyl, n-octadecyl, n-octadecenyl, orn-octadecadienyl and R is an aliphatic hydrocarbon radical containing 1to 18 carbon atoms, such as methyl, ethyl or any of those comprising R.A specific example of a preferred anticlogging copolymer in which thenitrogen containing substituent is linked to the copolymer chain throughan ester linkage is the 1:9 copolymer of di(Oxo-octyl)aminoethylmethacrylate and lauryl methacrylate, Specific examples of other suchcopolymers are the 0.05:1, 01:1, 0.5 :1, and 1:1 weight ratio copolymersof monomeric noctylaminoethyl, laurylaminoethyl, octadecylaminoethyl,and octadecenylaminoethyl acrylates and methacrylates, and monomericn-octyl, lauryl, Oxo-octyl, 2-ethylhexyl, Oxo-tridecyl, and n-hexadecylacrylates and methacrylates.

The preferred supplemental, nitrogenous, anticlogging copolymers,disclosed herein are copolymers of the aboveindicated monomers in weightratios in the range of about 0.05 to 0.75 part by weight of nitrogencontaining monomer to one part by Weight of nitrogen-free ester monomer.

The average molecular weight of the anticlogging copolymers disclosedherein will normally be greater than about 2,000 and preferably greaterthan about 7,500, as determined by conventional methods. Usually themolecular weight of the copolymers will not exceed about 500,000 but themolecular weights can be greater, provided that the molecular weight isnot so great as to render the copolymer insoluble in the liquidhydrocarbon fuel distillates disclosed herein.

The oil-soluble, supplemental, anticlogging phosphosulfurizedhydrocarbon reaction products suitable for the purposes of thisinvention can be prepared in any convenient manner. For example, thesematerials can be prepared by reacting a sulfide of phosphorus with analiphatic hydrocarbon in relative proportions and at reaction conditionssuificient to effect reaction of all of the phosphorus sulfide. Thus,good results are obtainable by effecting the reaction at a temperatureof about 200 to 600 F., preferably about 300 to 500 F., using a moleratio of about 1 to 10, preferably about 2 to 5, molecular proportionsof hydrocarbon for each molecular proportion of the phosphorus sulfide,usually in an inert atmosphere, until substantially all of thephosphorus sulfide has reacted, usually about 2 to 10 hours. Althoughphosphorus pentasulfide is the preferred phosphorus sulfide, otherphosphorus sulfides such as P 8 P 8 P487, or mixtures thereof can beused. The hydrocarbons starting materials include aliphatic hydrocarbonssuch as parafiins, olefins, olefin polymers, or petroleum fractions.Examples of such materials include di is-o'butylene, dodecene, andoctadecene. Examples of suitable olefin polymers are those havingmolecular weights of about 50 to 10,000, examples of which are polymersof ethylene, propylene, butylene, isobutylene, and the like orcopolymers of combinations of such monoolefins. An example of apreferred olefin polymer is :pentapropylene. An example of a preferredphosphosulfurized hydrocarbon is the 0.82:3.28 mol ratio reactionproduct of P 3 and pentapropylene obtained at a reaction temperature of220 C. over a period of about 4.5 hours. An example of another suchreaction product is the reaction product of a SUS Mid-Continent brightstock and 10 percent by weight P 8 The diethylene glycol monoesters, aswell as the supplemental anticlogging agents, when they are used, can beincorporated in combustion gas turbine fuels in any suitable manner. Forexample, they can be added singly or in combination, either as such, orin diluted form to the fuels either promptly after distillation or afterstorage for an indefinite period of time. When the diethylene glycolmonoesters and the supplemental anticlogging agents are added to thefuels in admixture it frequently will be advantageous to add the agentsin the form of a concentrated solution, say, a 50 percent solution, in asolvent such as Oxo-octyl alcohol or other suitable solvent, as theaddition agents disclosed herein are frequently not otherwise mutuallysoluble. Alternatively, the addition agents disclosed herein can beadded to aviation turbine fuels in admixture with other addition agentsadapted to improve one or more characteristics of the fuels. Forexample, the addition agents disclosed herein can be added to the fuelsin admixture with corrosion inhibitors, such as, amine salts of organicesters of orthophosphoric acid, antioxidants such as2,6-di-tertiarybutyl-4-methylphenol, or2,4-dimethyl-6-tertiary-butylphenol.

The diethylene glycol monoesters disclosed herein can be employed inaviation combustion gas turbine fuels in any proportions sufiicient toimprove the thermal stability of the fuels. A noticeable improvement inthermal stability, especially as regards reduction of heat transfersurface deposits, normally will be obtained by the use of as little as2.5 pounds of diethylene glycol monoester per thousand barrels of fuel,but it is usually desirable to employ at least five pounds per thousandbarrels of fuel of the diethylene glycol monoester in order to obtain asubstantial improvement in thermal stability. A major improvement willordinarily be obtained by the use of proportions in the range of about10 to pounds .per thousand barrels of fuel. No additional benefits,insofar as thermal stability is concerned, are obtained with greaterproportions. When a supplemental anticlogging agent of the kinddisclosed herein is employed in the fuel, these materials can be used inthe same range of proportions as the diethylene glycol monoesters andthe respective materials can be employed in varying proportions withrespect to one another. Normally, it is preferred to employ thediethylene glycol monoesters and the supplemental anticlogging agents inapproximately equal proportions, but this is not essential as otherrelative proportions can be employed, provided that each of therespective agents is employed in proportions of at least 2.5 pounds ofagent per 1,000 barrels of fuel. By way of illustration, the diethyleneglycol monoesters and the supplemental anticlogging agents can beemployed in weight ratios of about 1:8 to 8:1, and preferably 1:4 to4:1.

Combustion gas turbine fuels of the type Whose use is included by thisinvention are liquid hydrocarbon mixtures, typical of which are ordinaryaviation turbine fuels, that is, jet fuels. The properties of the mostcommon aviation turbine fuels are defined fully in the followingspecifications: MIL-J-5161E (Referee JP4 Fuel), MIL-J-5624D (JP-4, JP5Fuel), MIL-F- 656 (JP-6 Fuel), MIL-F-25524A (Thermally Stable Fuel),MIL-F25558B (RI-1 Fuel), MIL-R-25576B (RP1 Fuel), and American AirlinesSpecification No. M6-4A. In general, aviation turbine fuels arecharacterized by the following common properties:

Gravity, API 32.5-57.

Existent gum, mg./l00 ml. (max.) 5-7.

Potential gum, mg./100 ml. (max.) 4-14.

Sulfur, percent (max.) 0.05-0.4.

Mercaptan sulfur, percent (max.) 0.0010.005.

Freezing Point, F. (max.) 75 to 40.

Thermal value, B.t.u. l-b. (min.) 18,30018,500.

Aniline-gravity constant 4,500, usually Aromatics, vol. percent (max.)5-25.

Olefins, vol. percent (max.) 1-5.

In addition to these characteristics, it also may be noted that typicalaviation turbine fuels employed for use in aviation turbine enginesinvolving a high temperature fuel stability problem normally boil in therange of 250 F. to 700 F., that is to say, aviation turbine fuelsnormally boil above the gasoline range.

The ability of the materials disclosed herein to reduce formation ofsolid deposits in aviation turbine fuels at high service temperatureshas been demonstrated by subjecting representative fuel compositions ofthe kind disclosed herein to the CFR Fuel Coker test procedure. Thistest procedure is described in detail in the Manual of ASTM Standards onPetroleum Products, ASTM D- 1660-59T. In accordance with this testmethod, aviation turbine fuels are subjected to flow conditions andtemperature stresses similar to those in combustion gas turbine or jetaircraft engines by circulation through a simulated aircraft fuelsystem, maintained at a temperature in excess of 300 F., at a rate ofsix pounds of fuel per hour for a period of 300 minutes. The testapparatus comprises a fuel system containing two heated sections, one ofwhich is a preheater section that simulates the hot fuel line sectionsof an aviation turbine engine as typified by the engine fuel-lubricatingoil cooler. The extent of fouling of heat transfer surfaces in thepreheater section by fuel degradation deposits is determined byinspection, and the extent of such fouling is used as one index of thehigh temperature stability of the aviation turbine fuel in the heatexchanger section of an aviation turbine engine. Preheater deposits arerated according to the following scale: 0=no visible deposits; 1=visiblehaze or dulling, but no visible color; 2=barely visible coloration;3='light tan to peacock stain; 4=heavier than 3.

The second heated section comprises a filter section that simulates thenozzle area, or fuel inlet area of the combustion zone of a jet enginewhere fuel degradation particles may be trapped. A precision, sinteredstainless steel filter is employed in the filter section to trap fueldegradation particles formed during the test. The extent of the buildupof fuel degradation particles in the filter section is indicated by thepressure differential across the test filter, and this pressuredifferential is used as another in dex of the high temperature stabilityof the aviation turbine fuel. In carrying out the tests described, thetemperature of the fuel at the outlet of the preheater section ismaintained at 410 F. and the filter section temperature is maintained at500 F.

In the fuel compositions subjected to the above-described test, thediethylene glycol monoester was a commercial material, Emcol RDC-D whichwas found to contain 89 percent diethylene glycol monolaurate and 11percent ionized carboxylates composed of 50 mole percent lauric acid, 30mole percent myristic acid, 15 mole percent palrnitic acid, and 5 molepercent stearic acid. One of the supplemental anticlogging agentsemployed in the test was the 1:9 weight ratio copolymer of di(OXo-octyl)aminoethyl methacrylate and lauryl methacrylate. This material wasprepared by heating a mixture of 55 grams di(Oxo-octyl)aminoethylmethacrylate, 495 grams lauryl methacrylate, 3.3 gramsazodiisobutyronitrile and 1100 grams of an SAE 10/W lubricating oil,with stirring, in a stream of nitrogen for six hours at 55 C. Theresulting copolymer was obtained in a viscous solution slightly lighterin color than the solvent oil. The calculated nitrogen content of 0.13for the solution was confirmed by analysis. A similarly prepared,oil-free copolymer had an average molecular weight of about 180,000. The0x0- octyl su-bstituents of the di(Oxo-octyl)aminoethyl methacrylatewere derived from Oxo-octyl alcohol, that is, octyl alcohol prepared bythe Oxo synthesis process. A typical sample of the Oxo-octyl alcoholfrom which the substituents were derived contained about 38 percent4,5-dimethylhexyl alcohol, 30 percent 3,5-dimethylhexyl alcohol, 10percent S-methylheptyl alcohol, 19 percent 3,4-dimethylhexyl alcohol,and 3 percent 5,5-dimethylhexyl alcohol.

Another supplemental anticlogging agent employed in the tests describedherein was a nitrogenous copolymer prepared just as described aboveexcept for the substitution of Oxo-octyl methacrylate for laurylmethacrylate. Still another supplemental anticlogging agent was aphosphosulfurized hydrocarbon product obtained by reacting P 8 andpentapropylene in the mol ratio of 0.82:3.28 at about 220 C. for about4.5 hours.

In the tests reported below, the test fuels were commercial-typeaviation turbine fuels having the following characteristics:

Test fuel A Test fuel B Gravity: API 43. 7 43. 6 Freezing point: F 65 51Sulfur. L: percent 0. 011 0. 054 Mercaptan sulfur: pereent 0. 001 0. 001Existent gum: mg./l00 ml. 0. 3 1.6 Potential gum: mg./100 ml 1. 2 5. 2Aromatics: vol. percent. 14. 7 15. 7 Olefins: vol. percent 1. 0 1.7saturates: vol. percent 84. 3 82. 6 Thermal value: B.t.u./lb 18, 581 18,587 Aniline-Gravity Constant.-. 6, 337 6, 444 Distillation, keroseue'Over point: F 354 330 End point: F 514 524 10% evap. at- 368 372 50%evap. at 398 90% evap. at- 452 484 The make-up of the test samples andthe results obtained in the above-described tests were as set forth inthe following table:

Table A 10 Table B It will be understood that the invention is notlimited to the particular diethylene glycol monoesters or supplecificembodiments, and that other materials disclosed herein can also beemployed with good results. For example, for the supplementalanticloggin-g agents of the preceding sp cific embodiments there can besubstituted in p portions of, for example, 10 to 20 pounds per thousandbarrels Makeup-Percent by Volume:

Aviation Turbine Fuel A- Aviation Turbine Fuel B. StabilizerAddedLb./1000 Diethylene Glycol Monolaurate 1:9 wt. ratio eopolymerDi(Oxo-octyl)arm'noethyl methacrylate and lauryl methacrylate.

1:9 wt. ratio oopolymer Di(0xo-octyl)aminoethyl methacrylate andOxo-octyl methacrylate.

P s -pentapropylene reaction product Inspections:

Thermal stability, OFR

Fuel Coker:

Filter Section:

Time to reach a pressure drop of 10 In. HgzMin Time to reach a pressuredrop of in. Hgzmin AP at 300 min: in. Hg Preheater Section:

Maximum preheater deposit rating Average preheater deposit rating.

From a comparison of results obtained in Test Runs 1 and 2, it will beseen that incorporation of a small amount of diethylene glycolmonolaurate in aviation turbine fuel completely eliminated preheaterdeposits, i.e., heat transfer surface deposits. Comparison of theresults obtained in Test Runs 1 and 3 and the results obtained in TestRuns 4 and 5, 6 and 7 indicates that the combination of the diethyleneglycol monolaurate and the supplemental anticlogging agents elfectedessentially complete reduction of both preheater section, or heattransfer surface deposits, and the filter section deposits. The factthat the polymeric anticlogging agents reduce the filter clogging actionof the diethylene glycol monolaurate without diminishment of thedesirable characteristics of the latter indicates a coaction between thematerials, as not every material that is capable as such of reducingfilter section deposits retains its effectiveness in the presence ofpreheater deposit inhibitors such as the diethylene glycol monolaurate.

Examples of other fuel compositions included by the invention are setforth in the following table:

of fuel, quaternary ammonium salt copolymers such as the 1:9 weightratio copolyme-rs of monomeric distearyldimethylammonium methacrylateand monomeric lauryl methacrylate and the 0.0501, the 01:1, the 0.521,and 1:1 weight ratio copolymers of monomericdioctadecenyldimethylam'monium, octadecenyldimethylethylammonium,distearyldimethylammonium, laurylbenzyldimethylammonium,lauryldimethyl(ethylbenzyl)ammonium acrylates and methacrylates, andmonomeric n-Octyl, lauryl, OX0- octyl, 2-ethylhexyl, Oxo-t-ridccyl, andn-hexadecyl acrylates and methacrylates; addition salt copolymers suchas the 3:7 Weight ratio copolymer of monomeric di(OXo- -octyl)am1noniummethacrylate and monomeric lauryl methacrylate, the 1:9 Weight ratiocopolymer of monomeric di(Oxo-octyl)hydroxyethylammonium methacrylateand monomeric lauryl methacrylate, and the 0.05 :'1, 0.1: l, 0.5 :1, and1:1 weight ratio copolymers of monomeric octylammonium,dioctylamrnonium, trioctylammonium, laurylammonium, octadecylammonium,octadecenylammonium acrylates and methacrylates and monomeric n-octyl,lauryl, Oxo-octyl, Z-ethylhexyl, Oxo-tridecyl, and

n-hexadecyl acrylates and methacrylates; or aminoester copolymers suchas the 0.05:1, 0.1:1, :1, and 1:] weight ratio copolymers of monomericn-octylaminoethyl, laurylaminoethyl, octadecylaminoethyl, andoctadecenylaminoethyl acrylates and methacrylates.

In addition to their remarkable stabilizing characteristics, theimprovement agents disclosed herein are distinguished by the fact thatthey impart unusually good water separation properties to combustion gasturbine engine fuels; that is, they do not promote or permit significant emulsification of water and fuel. Moreover, the preferred fuelcompositions of this invention are advantageous in that they areessentially free from metallic ashforming materials, neglectingimpurities, especially heavy metal ash-forming materials, whereby theydo not accelerate development of combustion deposits in engines in whichthey are consumed.

The combustion gas turbine fuel compositions of this invention can alsocontain various other addition agents adapted to improve one or moreproperties of the fuel. For example, the fuel compositions of thisinvention can contain in addition to the addition agents disclosedherein, corrosion inhibitors, freezing point depressants, antioxidants,metal deactivators, combustion and/ or ignition improvement agents andthe like.

Many modifications and variations of the invention as herein describedwill suggest themselves to those skilled in the art and resort may behad to such modifications and variations without departing from thespirit and scope of the invention. Accordingly, only such limitationsshould be imposed as are indicated in the claims appended hereto.

We claim:

1. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, suflicient to improve the thermal stability of said fuel, of acombination of (A) a monoester of a fatty acid containing 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) an oil-solublenitrogen containing anticlogging copolymer of (i) a monomericcopolymerizable alkyl ester of an acid selected from the groupconsisting of acrylic and lower alkacrylic acids whose alkyl estersubstitutents contains 8 to 18 carbon atoms, and (ii) a monomeric,copolymerizable unsaturated compound containing an ethylenic linkage asthe sole functional group that is copolymerizable with the aforesaidmonomeric alkyl ester and a nitrogencontaining substituent group, saidmonomeric components being present, respectively, in the copolymer in aweight ratio of about 0.03 :1 to 1:1, said small amount comprising atleast about 2.5 pounds of each member of said combination per thousandbarrels of fuel, and the members are present in the composition in aweight ratio with respect to each other of about 8:1 to about 1:8.

2. The composition of claim 1 where said small amount comprises about topounds of each member of said combination per thousand barrels of fuel,and the members are present in the composition in approximately equalweight proportions.

3. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufiicient to improve the thermal stability of said fuel of acombination of (A) a monoester of a fatty acid having 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) an oilsolublenitrogen-containing anticlogging copolymer of (i) a monomeric,copolymerizable alkyl ester of an acid selected from the groupconsisting of acrylic and lower alkacrylic acids whose alkyl estersubstituent contains 8 to 18 carbon atoms, and (ii) a monomeric,copolymerizable ester of an acid selected from the aforesaid group andan amine having as at least one N-substituent an alkylol groupcontaining 2 to 4 carbon atoms and as another N-substituent an aliphatichydrocarbon radical containing 1 to 18 carbon atoms and as anotherN-substituent a member selected from the group consisting of hydrogen,aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms andalkylol radicals containing 2 to 4 carbon atoms, said monomericcomponents being present, respectively, in the copolymer in a weightratio of about 0. 05 :1 to 0.75: 1, said small amount comprising atleast about 2.5 pounds of each member of said combination per thousandbarrels of fuel, and the members are present in the composition in aweight ratio with respect to eachother of about 8:1 to about 1:8.

4. The composition of claim 3 where said small amount comprises about 10to 20 pounds of each member of said combination per thousand barrels offuel, and the members are present in the composition in approximatelyequal weight proportions.

5. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufficient to improve the thermal stability of said fuel, of acombination of (A) a monoester of lauric acid and diethylene glycol, and(B) an approximately 1:9 Weight ratio copolymer of (i)di(Oxo-octyl)aminoethyl methacrylate and (ii) lauryl methacrylate, saidsmall amount comprising about 5 to 20 pounds of each member of saidcombination per thousand barrels of fuel, said members being present inthe composition in a weight ratio with respect to each other of about 6.A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufiicient to improve the thermal stability of said fuel, of acombination of (A) a monoester of lauric acid and diethylene glycol, and(-B) an approximately 1:9 weight ratio copolymer of (i)di(Oxo-octyl)aminoethyl methacrylate and (ii) Oxooctyl methacrylate,said small amount comprising about 5 to 20 pounds of each member of saidcombination per thousand barrels of fuel, said members being present inthe composition in a weight ratio with respect to each other of about4:1 to 1:4.

7. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufiicient to improve the thermal stability of said fuel, of acombination of (A) a monoester of lauric acid and diethylene glycol, and(B) a phosphosulfurized pentapropylene product, said small amountcomprising about 5 to 20 pounds of each member of said combination perthousand barrels of fuel, said members being present in the compositionin a weight ratio with respect to each other of about 4:1 to 1:4.

8. A process for reducing formation of carbonaceous deposits bythermally unstable hydrocarbon oils on hot, heat transfer surfaces,comprising incorporating in a normally thermally unstable liquidhydrocarbon combustion gas turbine fuel that normally tends to formdeposits upon hot, heat transfer surfaces contacted thereby, prior tocontact with said heat transfer surfaces, a small amount, suflicient toreduce deposit formation of a monoester of a fatty acid containing 8 to18 carbon atoms per molecule and diethylene glycol, and then heating thefuel by contact with a heat transfer surface at a temperature in excessof 300 F.

9. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufficient to improve the thermal stability of said fuel, of acombination of (A) a monoester of a fatty acid containing 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) an oil-solublenitrogen-containing anticlogging copolymer of (i) a monomeric,copolymerizable alkyl ester of an acid selected from the groupconsisting of acrylic and lower alkacrylic acids whose alkyl estersubstituent contains 8 to 18 carbon atoms, and- (ii) a monomeric,copolymerizable unsaturated compound containing an ethylenic linkage asthe sole functional group that is copolymerizable with the aforesaidmonomeric alkyl ester, and also having a nitrogen-containing substituentassociated with the group containing the copolymerizable ethyleniclinkage through a linkage selected from the group consisting of ester,amine addition salt, amido and quaternary ammonium linkages, saidmonomeric components being present, respectively, in the copolymer in aweight ratio of about 0.03:1 to 1:1, said copolymer having an averagemolecular weight in the range of about 2,000 to about 500,000, saidsmall amount comprising at least about 2.5 pounds of each member of saidcombination per thousand barrels of fuel, and said members being presentin the composition in a weight ratio with respect to each other of about8:1 to about 1:8.

10. The composition of claim 9 where said small amount comprises about10 to 20 pounds of each member of said combination per thousand barrelsof said fuel, and the members are present in the composition inapproximately equal weight proportions.

11. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufficient to improve the thermal stability of said fuel, of acombination of (A) a monoester of a fatty acid containing 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) a member selected fromthe group consisting of (1) an anticlogging oil-solublephosphosulfurized aliphatic hydrocarbon selected from the groupconsisting of parafiins, olefins, petroleum fractions and olefinpolymers having molecular weights in the range of about 50 to 10,000,and (2) an oil-soluble nitrogen-containing anti-clogging copolymer of(i) a monomeric, copolymerizable alkyl ester of an acid selected fromthe group consisting of acrylic and lower alkacrylic acids whose alkylester substituent contains 8 to 18 carbon atoms and (ii) a monomeric,copolymerizable unsaturated compound containing an ethylenic linkage asthe sole functional group that is copolymerizable with the aforesaidmonomeric alkyl ester, and also having a nitrogen-containing substituentassociated with the group containing the copolymerizable ethyleniclinkage through a linkage selected from the group consisting of ester,amine addition salt, amido and quaternary ammonium linkages, saidmonomeric components being present, respectively, in the copolymer in aweight ratio of about 0.03:1 to 1:1, said copolymer having an averagemolecular weight of about 2,000 to about 500,000, said small amountcomprising at least about 2.5 pounds of each member of said combinationper thousand barrels of fuel.

12. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, suflicient to improve the thermal stability of said fuel of acombination of (A) a monoester of a fatty acid having 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) an oil-solublenitrogen-containing anticlogging copolymer of (i) a monomeric,copolymerizable alkyl ester of an acid selected from the groupconsisting of acrylic and lower alkacrylic acids whose alkyl estersubstituent contains 8 to 18 carbon atoms, and (ii) a monomeric,copolymerizable ester of an acid selected from the aforesaid group andan amine having as at least one N-substituent an alkylol groupcontaining 2 to 4 carbon atoms and as another N-substituent an aliphatichydrocarbon radical containing 1 to 18 carbon atoms and as anotherN-substituent a member selected from the group consisting of hydrogen,aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms andalkylol radicals containing 2 to 4 carbon atoms, said monomericcomponents being present, respectively, in the copolymer in a weightratio of about 0.05:1 to 0.75:1, said copolymer having an averagemolecular weight in the range of about 2,000 to about 500,000, saidsmall amount comprising at least about 2.5 pounds of each member of saidcombination per thousand barrels of fuel, and said members being presentin the composition in a weight ratio with respect to each other of about8:1 to about 1:8.

13. The composition of claim 12 Where said small amount comprises about10 to 20 pounds of each member of said combination per thousand barrelsof fuel, and the members are present in the composition in approximatelyequal weight proportions.

14. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufficient to improve the thermal stability of said fuel, of acombination of (A) a monoester of lauric acid and diethylene glycol, and(B) an approximately 1:9 weight ratio copolymer of (i)di(Oxo-octyl)aminoethyl methacrylate and (ii) lauryl methacrylate, saidcopolymer having an average molecular weight in the range of about 2,000to about 500,000, said small amount comprising about 5 to 20 pounds ofeach member of said combination per thousand barrels of fuel, saidmembers being present in the composition in a weight ratio with respectto each other of about 4:1 to 1:4.

15. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, suflicient to improve the thermal stability of said fuel, of acombination of (A) a monoester of lauric acid and diethylene glycol, and(B) an approximately 1:9 weight ratio copolymer of (i)di(OXo-octyl)aminoethyl methacrylate and (ii) Oxo-octyl methacrylate,said copolymer having an average molecular weight in the range of about2,000 to about 500,000, said small amount comprising about 5 to 20pounds of each member of said combination per thousand barrels of fuel,said members being present in the composition in a weight ratio withrespect to each other of about 4:1 to 1:4.

16. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufficient to improve the thermal stability of said fuel, of acombination of (A) a monoester of a fatty acid containing 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) an anticloggingoil-soluble phosphosulfurized aliphatic hydrocarbon selected from thegroup consisting of paraffins, olefins, and olefin polymers havingmolecular weights in the range of about 50 to 10,000, said small amountcomprising about 2.5 to 20 pounds of each member of said combination perthousand barrels of fuel, and the members are present in the compositionin a weight ratio with respect to each other of about 8:1 to 1:8.

17. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufficient to improve the thermal stability of said fuel, of acombination of (A) a monoester of a fatty acid containing 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) a member selected fromthe group consisting of 1) an anti-clogging oil-solublephosphosulfurized aliphatic hydrocarbon selected from the groupconsisting of parafiins, olefins, and olefin polymers having molecularweights in the range of about 50 to 10,000 and (2) an oil-solublenitrogen-containing anti-clogging copolymer of (i) a monomeric,copolymerizable alkyl ester of an acid selected from the groupconsisting of acrylic and lower alkacrylic acids whose alkyl estersubstituent contains 8 to 18 carbon atoms, and (ii) a monomericcopolymerizable unsaturated compound containing an ethylenic linkage asthe sole functional group that is copolymerizable with the aforesaidmonomeric alkyl ester and having a nitrogen-containing substituentgroup, said monomeric components being present, respectively, in thecopolymer in a weight ratio of about 0.03 to 1:1, said small amountcomprising at least about 2.5 pounds of each member of said combinationper thousand barrels of fuel.

18. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, sufiicient to improve the thermal stability of said fuel, of acombination of (A) a monoester of a fatty acid containing 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) an anti-cloggingoil-soluble phosphosulfurized aliphatic hydrocarbon from a petroleumfraction, said small amount comprising about 2.5 to 20 pounds of eachmember of said combination per thousand barrels of fuel, and the membersare present in the composition in a weight ratio with respect to eachother of about 8:1 to 1:8.

19. A fuel composition comprising a major amount of a normally thermallyunstable liquid hydrocarbon combustion gas turbine fuel and a smallamount, suflicient to improve the thermal stability of said fuel, of acombination of (A) a monoester of a fatty acid containing 8 to 18 carbonatoms per molecule and diethylene glycol, and (B) a member selected fromthe group consisting of (1) an anti-clogging oil-solublephosphosulfurized aliphatic hydrocarbon from a petroleum fraction, and(2) an oilsoluble nitrogen-containing anticlogging copolymer of (i) amonomeric, copolymerizable alkyl ester of an acid selected from thegroup consisting of acrylic and lower alkacrylic acids whose alkyl estersubstituent contains 8 to 18 carbon atoms, and (ii) a monomericcopolymerizable unsaturated compound containing an ethylenic link age asthe sole functional group that is copolymerizable with the aforesaidmonomeric alkyl ester and having a nitrogen-containing substituentgroup, said monomeric components being present, respectively, in thecopolymer in a weight ratio of about 0.03 to 1: 1, said small amountcomprising at least about 2.5 pounds of each member of said combinationper thousand barrels of fuel.

20. The composition of claim 16 Where said small amount comprises about10 to 20 pounds of each member of said combination per thousand barrelsof fuel, and the members are present in the composition in approximatelyequal Weight proportions.

References Cited by the Examiner UNITED STATES PATENTS 2,527,889 10/1950Moore et a1. 252-56 X 2,737,452 3/1956 Catlin et a1. 4462 2,768,99910/1956 Hill 252--32.7 X 2,800,452 7/1957 Bondi et a1. 4462 X FOREIGNPATENTS 131,778 3/ 1949 Australia.

701,459 12/1953 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

LEON D. ROSDOL, Examiner.

17. A FUEL COMPOSITION COMPRISING A MAJOR AMOUNT OF A NORMALLY THERMALLYUNSTABLE LIQUID HYDROCARBON COMBUSTION GAS TURBINE FUEL AND A SMALLAMOUNT, SUFFICIENT TO IMPROVE THE THERMAL STABILITY OF SAID FUEL, OF ACOMBINATION OF (A) A MONOESTER OF A FATTY ACID CONTAINING 8 TO 18 CARBONATOMS PER MOLECULE AND DIETHYLEEN GLYCOL, AND (B) A MEMBER SELECTED FROMTHE GROUP CONSISTING OF (1) AN ANTI-CLOGGING OIL-SOLUBLEPHOSPHOSULFURIZED ALIPHATIC HYDROCARBON SELECTED FROM THE GROUPCONSISTING OF PARAFFINS, OLEFINS, AND OLEFIN POLYMERS HAVING MOLECULARWEIGHTS IN THE RANGE OF ABOUT 50 TO 10,000 AND (2) AN OIL-SOLUBLENITROGEN-CONTAINING ANTI-CLOGGING COPOLYMER OF (I) A MONOMERIC,COPOLYMERIZABLE ALKYL ESTER OF AN ACID SELECTED FROM THE GROUPCONSISTING OF ACRYLIC AND LOWER ALKACRYLIC ACIDS WHOSE ALKYL ESTERSUBSTITUENT CONTAINS 8 TO 18 CARBON ATOMS, AND (II) A MONOMERICCOPOLYMERIZABLE UNSATURATED COMPOUND CONTAINING AN ETHYLENIC LINKAGE ASTHE SOLE FUNCTIONAL GROUP THAT IS COPOLYMERIZABLE WITH THE AFORESAIDMONOMERIC ALKYL ESTER AND HAVING A NITROGEN-CONTAINING SUBSTITUENTGROUP, SAID MONOMERIC COMPONENTS BEING PRESENT, RESPECTIVELY, IN THECOPOLYMER IN A WEIGHT RATIO OF ABOUT 0.03 TO 1:1, SAID SMALL AMOUNTCOMPRISING AT LEAST ABOUT 2.5 POUNDS OF EACH MEMBER OF SAID COMBINATIONPER THOUSAND BARRELS OF FUEL.